Flash gettering method and apparatus having pulse duration control



March 12, 196s W. M. GRIMES, JR 3,372,96

FLASH GETTERING METHOD AND APPARATUS HAVING PULSE DURATION CONTROL FiledOct. 29, 1964 3 Sheets-Sheet 1 l Y @EN ISEE s u `i 5 Of Sx k1 li S Utk ot 05;@ T Q- lu \l l V7 s l o K Q (l 0R t: O

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FLASH GETTEmNG ME Filed Oct. 29, 1964 3 Sheets-Sheet 2 FRoMfRsGGf-:R F}G2 /177'0 RNE March 12, 1968 w. M. GRxMEs, JR 3,372,958

FLASH GETTERlNG METHOD AND APPARATUS HAVING PULSE DURATION CONTROL Filedoct. 29, 1964 s sheets-sheet s l Il] T A no' :il &::

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United States Patent C) 3,372,968 FLASH GETTERING METHOD AND APPARATUSHAVING PULSE DURATION CONTROL Willard M. Grimes, Jr., Bloomfield, NJ.,assignor to Westinghouse Electric Corporation, East Pittsburgh,

Pa., a corporation of Pennsylvania Filed Oct. 29, 1964, Ser. No. 407,29517 Claims. (Cl. S16-25) ABSTRACT OF THE DISCLOSURE A lamp getteringmethod and apparatus which provides a series of constant current pulsesof predetermination duration and magnitude through a filament sufficientto flash getter material from the filament but insufiicient to cause thefilament to recrystallize and thus become brittle. The IR drop acrossthe filament is sensed, compared to a maximum permissible value and theduration of the constant current pulses controlled to maintain the IRdrop across the filament and hence the getter flashing temperature at apredetermined level.

The present invention relates to lamps and, more particularly, to anelectronic flashing control apparatus and method having particularapplication to the flashing of an electric lamp to activate thecustomary getter by heating the filament to a uniform temperature.

In order to getter electric lamps it is necessary to flash the lamp byheating the filament to a temperature sufficient to activate the getter.When so activated, the getter then combines with the residual impuritiesremaining in the lamp after it has been evacuted. Heretofore nosatisfactory and dependable Way has been known to maintain the lampfilament at a uniform predetermined temperature during gettering withthe result that too frequently the filament temperature was raised tothe recrystallization point resulting in fragile and saggy lilaments. Bythe flashing control system of the present invention, the flashing ofthe getter is accomplished in less time than heretofore, by maintainingthe temperature of the filament uniform during flashing. This isachieved by subjecting such filament to a constant preselected currentas a function of desired temperature thus eliminating the possibility offilament recrystallization with ensuing fragility and sagging.

The problem of getter flashing has been particularly severe withminiature-type, evacuated lamps since a relatively large amount ofgetter must be completely flashed from the very fine filament during thelamp fabrication. In the case of Christmas tree lamps, the fabricatedlamp must be coated with a color filter, and the shocks encounteredduring coating have resulted in an undue amount of product shrinkagebecause of the brittle, recrystallized filaments. In the past, suchlamps have usually been hand packed because of the brittle filaments anda large amount of customer' breakage has resulted when these lamps weresold loose from bins or store counters.

It is accordingly the primary object of the present inventon to providean improved method and apparatus for flashing the getter duringfabrication of an electric lamp and which consistently produces strongerfilaments than heretofore,

Another object of the present invention is the provision of anelectronic flashing control system which applies constant current to thelamp lament throughout each flash.

A further object of the present invention is the provision of anelectronic flashing control system for the 3,372,968 Patented Mar. 12,1968 flashing of a getter in an electric lamp during its fabricationwherein the duration of the arc in each flash is controlled.

An additional object is to provide an incandescent, evacuated lamp,preferably of the miniature type, which can be handled readily either inthe factory or by the customer, without breaking the filament.

The foregoing objects of the present invention, together with otherobjects which will become apparent to those skilled in the art from thefollowing description, lare achieved by providing a flashing controlmethod and apparatus which senses the character of current flow throughthe lamp during gettering and distinguishes between gaseous and metallicconduction. Thereupon the gaseous conduction is kept within safe timelimits and the metallic conduction within safe but effective voltagelimits, which voltage limits together indicate the maximum instantaneoustemperature limits that a filament may reach during flashing, underutilization of constant current control as a measure thereof. There isalso provided the resulting product.

The present invention can be more readily understood by reference to theaccompanying drawings wherein:

FIGURE l is a block diagram illustrating various parts of the electronicflashing control of the present inventiontion and showing the shape ofthe wave as produced by such circuit part,

FIGURE 2 is a diagram of the circuitry of the electronic flashingcontrol system, and

FIGURE 3 is a graphic illustration of the shape of the current, voltageand temperature waves as produced by the electronic flashing circuit asshown in FIG. 2.

The following constitutes a brief outline of the operation of thepresent system. The incandescent filament which is being flashed isformed of 'tungsten and displays an electrical resistance whichincreases sharply with increasing temperature. When a constant currentof given magnitude is passed through a cold tungsten filament, theresulting IR drop across the filament will be relatively small, sincethe filament electrical resistance is low. When the same constantcurrent is passed through a hot filament, however, the resulting IR dropacross the filament will be relatively large, since the filamentresistance is now correspondingly high. The apparatus comprises acurrent supply means for passing through the filament a series ofconstant current pulses of predetermined duration and magnitude. Thesepulses rapidly heat the filament to a predetermined temperaturesufficient to flash etter material from the filament, but whichtemperature is insufficient to cause the filament to recrystallize andthus become brittle. This constant current supply means comprises thetrigger pulse generator 5, the ON square Wave generator 7, the OR gate9, and the current regulator 12, as shown in block diagram in FIG. l.

There is also provided a voltage detecting and signalling means whichresponds to the IR drop developed across the lamp filament when theconstant current pulses are passed |therethrough. The voltage detectingIand signalling means acts to generate a control signal when the IR dropdeveloped across the heated lament reaches a predetermined value whichsignifies that the filament getter flashing temperature has beenachieved. The voltage detecting and signalling means comprises thecut-off voltage reference or voltage leveler 17 and the voltagecomparator 15, las shown in FIG. l.

A current pulse control means responds to the control signal generatedby the above-noted voltage detecting and signalling means to shorten theduration of each constant current pulse passed through the lamp filamentby the above-noted current supply means. This decreases the averagewattage consumed by the filament by such amount that the resulting IRdrop across the filaments during each such shortened constant currentpulse, is maintained substantially at that predetermined value whichindicates that the predetermined filament getter flashing temperaturehas been achieved. The current pulse control means comprises the OFFsquare wave generator 10 working through the OR gate 9 to limit theduration of each constant current pulse supplied to the lamp filament bythe current regulator, as shown in FIG. l.

Finally, a timing means comprising the switch 24 and associated cam, asshown in FIG. 2, operates to control the above-noted current supplymeans to pass constantcurrent pulses through the lamp filament for apredetermined time which is sufcient to completely fiash the gettermaterial from the lamp filament.

Referring now to the drawings in detail the trigger pulse generator ofFIG. 1 comprises a standard multivibrator circuit with its timeconstants adjusted to give av desired trigger pulse repetition rate of500 pulses per second for a period of 1.6 seconds which are supplied tothe electric lamp during its approximately 2.4 seconds dwell at theget-ter flashing station, although such pulse repetition rate andduration period as supplied are not critic-al Iandcan be varied. Whenthe machine indexes a lamp to its getter flashing position, a switch isopened to cause the Wave form 6 thus generated, and as shown in FIG. l,to be thereafter transmitted to an ON square wave generator 7 which isoperable to emit a sign-al pulse of predetermined length. The length ofthis pulse is determined by a simple adjustmen-t of the time constantsof this ON square Wave generator, which latter comprises a standardone-shot multivibrator circuit producing a square wave form 8, `as shownin FIG. 1, with this signal pulse feeding one side of an OR gate 9.

The'OR gate 9 opens only when the ON pulse iS presenton one side ascontrolled by a timing circuit and an OFF square wave generator 10 hasnot signalled the other side of the OR gate. Also the OFF square wavegenerator 10 can close the OR gate 9 at any time, even while on ON pulseis still present on the other side of the OR gate. When the OR gate 9 isopen and con-ducting, a pulse 8 from the ON square wave gene-rator 7passes through the OR gate 9 and signals a current regulator 12 to passa rectangular pulse 13 of constant amplitude onto the lamp 14. Thiscurrent regulator 12 is a feedback amplifier circuit which allows thevoltage across` the lamp 14 to build up as its resistance increases, sothat the' voltage can increase from an initial twenty-five volts to overfour hundred volts without detrimentally effecting the operation of thecurrent regulator 12 to maintain the current through the lamp 14 at adesired constant level.

The voltage comparator 15 senses the instant that the voltage across thelamp 14 exceeds the cut-off level which ashereinafter described indetail is set at three hundred volts. At this 300 volts cut-off level,the Voltage comparator 15 triggers the OFF square wave generator whichsends a negative pulse 16 to the OR gate to close the latter andterminate that pulse, with the OFF pulse lasting until after the ONpulse has been completed. Before the next ON pulse arrives to the ORgate 9, Ithe negative OFF pulse ends and unlocks the OR gate so that itis opened by the next ON pulse.

Since the ON pulses last for 0.4-4 milliseconds, as shown by the Currentwave form in FIG. 3, and the current pulses as previously mentioned aresupplied to the lamp y14 at a rate of 500 pulses per second, the heatingeffect of these pulses on the lamp 14 is cumulative. Each pulseaccordingly imparts more heat to the filament than is lost by thefilament during the 1.56 millisecond interval between pulses with theresult that each such pulse paises the filamentof the lamp 14 to a stillhigher temperature as shown by the Temperature curve in FIG. 3. inasmuchas the current through the filament of lamp 14 is held 4 1 constant bythe current regulator 12, as also shown b the Current curve in FIG. 3,such temperature rise to a maximum of about 2100 C. (-FIG. 3) isaccompanied by a corresponding increase in its resistance. This resultsalso in a rise in the voltage across such heated filament, as shown bythe Voltage curve of FIG. 3, in accordance with Ohms law from about 25volts at room temperature to a cut-off Voltage across the lamp of 300volts,` as set by the Cut-Off Voltage Leveler 17 (FIG. 1).

Because the filament of the lamp 14 cools very little during the 1.56milliseconds interval between pulses, the succeeding pulses of 0.44milliseconds duration will bring 'the filament of the lamp 14 up to thevoltage cut-off of 300 volts in less than one second, as can be seenfrom both the Temperature and Voltage curves of FIG. 3. Once thisdesired temperature and itsrcorresponding voltage cut-off is reached thelength of each pulse in the train is automatically shortened, as seen bythe Current curve of FIG. 3. Thereafter the succeeding pulses will bringthe temperature and hence the voltage to its cut-off value of 300 voltsin less than one tenth of a millisecond with the remaining three or fourtenths of a millisecond of the ON pulse being suppressed by the OFFpulse.

By reference now more specifically to the circuit diagram of FIG. 2 itwill be noted that the lamp 14 when at its gettering position of thelamp making machine is adapted to receive energy from the CurrentRegulator 12. This regulator 12 comprises a 700 Volt Supply forenergizing the lamp 14 through a current regulator and feedbackamplifier tube V4 with the screen grid of such tu-be receiving a biasingpotential from a 280 Volt Screen Grid Supply under control of a tube V5.A variable resistor R43 is included in the energizing cir-f cuit for thelamp 14 and has one of its ends connected. by a conductor 22 to thenegative side L2 of a 450 Volt Supply source while the control grid ofcurrent regulator tube V4 is likewise connected by a conductor 23 to theplate electrodes of a constant current regulator tube V6 and through aresistor R21 to the cathode of a control tube V2 and one end of afurther resistor R22, all of which form part of the previously mentionedOR gate 9, and thence from the other end of resistor R22 to the negativeconductor L2.

During indexing movement of the lamp making machine, and hence from thetime a gettered lamp 14 is moved out of its station and a new lamp 14 ismoved into the gettering station, the signal from the conventionaltrigger pulse generator S (not shown) is rendered ineffective by closureof a cam-operated switch 24 which connects the supply conductors 25 and26 from such generator together, with a resistor R56 thereuponconstituting the sole pulse generator load. At this particular momentthe various elements of the circuit of FIG. 2 will be in a definiterelationship. For example, control tube V5 will be conducting and hencea potential is supplied to the screen grid of current regulator andfeedback amplifier tube V4, but due to the potential on the control gridof this tube it is non-conducting. The ON square wave generator tube V1is actually a dual tube, as are the remaining tubes in FIG. 2, andhereinafter the left-hand section of each such tube will be identifiedby the letter A and the right-hand section by the letter 13. At the sametime multivibrator ON tube V1B is conducting since its grid receives anappropriate potential relative to its cathode from a capacitor C1 whichhas been previously charged through a resistor R4. Thus current fiowsfrom the positive side L1 of the 450 Volt Supply through a resistor R5and tube section V1B to a common resistor R20 and back to negativesupply conductor L2; Due to the cathodes of both tube sections beingtied together, the same potential is imposed thereon and since thispotential is higher han that supplied to the grid of section VIA, thissection is then non-conducting.

At the same time that section of tube V1B is conducting the section V2Aof the cathode follower tube V2 of the OR gate 9 is likewise conducting.This is due to the fact that since there is conduction through R with avoltage drop thereacross, a lower potential is i-mpressed on the cathodeof a crystal diode CRZ than on its anode which is connected to thesupply conductor L1 through a resistor R7 and hence diode CR2 becomesconductive. This causes the ilow of current through diode CRZ with avoltage drop across resistor R7 and since the latter is connected to thegrid of tube section V2A the potential impressed thereon is lowered,Also, since this tube section is initially conducting with current flowfrom positive conductor L1 through tube section V2A` and previouslymentioned resistor R22 to the negative supply conductor L2, the ow ofcurrent through this resistor R22 is greatly reduced by lowering of thepotential on the grid of tube section V2A. This tube V2A being a cathodeIfollower with the load resistor R22 on the cathode side instead of itsanode side results in the tube automatically adjusting itself so thatits cathode always remains just a few volts above the potentialimpressed on its grid. Since the cathode of section V2A, as previouslymentioned, is connected through resistor R21 and conductor 23 to thegrid of current regulator and feedback amplier tube V4, whateverpotential the cathode of V2A assumes at any given moment, there will bea constant difference between that potential and the voltage supplied tothe grid of current regulator and feedback ampliiier tube V4.

Still during this period that cam-operated -switch 24 is closed and thetrigger pulse generator 5 is inoperative, the constant -currentregulator tube V6 of the OR gate 9 is conducting inasmuch as tubesection V2A, as previ- Ously mentioned, is now conducting andconsequently current flows from line conductor L1 to tube section V2A(by-passing resistor R7) and thence through parallel resistor R21 to theplates of regulator tube V6. Such current then iiows from the cathodesof tube V6 through common resistor R45 and a pair of resistors R51 andR53, through the negative conductor B2 from a 4510 Volt Bias Supply andthence through such bias supply to its positive conductor B1 which alsoconstitutes a negative conductor L2 for the 450 Volt Supply. 'Thevoltage on the cathodes of regulator tube V6 relative to its gridvoltages controls the flow of current therethrough so that this currentis constant. This constant current through constant resistor R21 therebyproduces a constant voltage drop thereacross so that any voltage changeon the cathode of OR gate tube V2A is faithfully reproduced at the lowerend of resistor R21 but at a lower D.C. voltage level. This lattervoltage is then supplied by the conductor 23 to current regulator andfeedback amplifier tube V4 as its grid bias and until the decreased flowof current through resistor R7 `imposes a higher voltage on the grid oftube section V2A and on its cathode, the additional drop throughresistor R21 causes the grid of tube V4 to render such tubenon-conducting and hence no current flows from the 700 Volt Supply tothe lamp 14.

It will be noted from FIG. 2 that the grids of the constant current ORregulator tube V6 are supplied with a potential from the 450 Volt BiasSupply through a potentiometer R32 and fixed resistors R51 and R53. Acapacitor C6 is connected across this bias supply source throughresistor R51 and similarly a pair of series connected voltage regulatortubes V8 and V9 are connected through the resistors R53 and R51 to thisbias supply source. The purpose of such resistors R51 and R53 togetherwith tubes V8 and V9 is to maintain a fixed voltage of 300 volts acrosssuch tubes V8 and V9 and it is a portion of the voltage from thisconstant source that is impressed upon the grids of the constant currentregulator tube V6 as selected lby the potentiometer R32. At the momentthat current regulator and feedback amplifier tube V4 is non-conductingthere is of course no current flow through lamp 14 and hence no voltagedrop thereacross. However, such lamp is connected by conductor 22 tothenegative side L2 of the 450 Volt Supply and hence is at ground potentialwhile the other side of the lamp 14 is likewise at ground potentialbeing connected to the negative side of the 700 Volt Supply and to thecathode of a crystal diode CR4. The anode of this diode CR4, however, issupplied with a negative potential as set by a potentiometer R36 of theCut-Off Voltage Leveler 17, which derives its voltage from conductor L2also common with positive bias conductor B1, and from negative biasconductor B2 through a resistor R55 and a conductor 29, so that when thelamp 14 is unenergized this crystal diode CR4 is non-conducting, Acapacitor C15 bridges this potentiometer and hence is connected to diodeCR4 as its load.

Prior to arrival of a pulse from trigger generator 5, the multivibratortube section V3A of the Ott Square Wave Generator 10 is conducting sincethe grid thereof is supplied with a high potential from a capacitor C17which has been previously charged through a potentiometer R12. A smallgrid current accordingly ows to the cathode and through a common cathoderesistor R24 to negative conductor B2 and thence through resistors R53and R51, then the 450 Volt Bias Supply to the positive bias conductorB1, and constituting also negative conductor L2, and through the 450Volt Supply back to conductor L1 thus completing the grid currentcircuit of tube section V3A. Simultaneously with this small grid currentfiow there will also be plate-cathode conduction with current flow fromsupply conductor L1 through resistor R10 to the plate of tube sectionV3A and from the cathode thereof through the same remaining portion ofthe above mentioned grid current circuit. Tube section VSB of the DitSquare Wave Generator 10 is rendered non-conducting at this time byvirtue of the voltage impressed upon the grid from potentiometer R17which is set at a lower voltage than that developed at the cathodes oftube V3 by the current flowing through resistor R24 during conductivityof tube section V3A and since tube section VSB is thus non-conducting nocurrent then flows through the plate resistor R44.

At the same time that tube section V3A is conducting there is a path ofcurrent ow from supply conductor L1 through a resistor R14 andpotentiometer R17 to the lower end of common cathode resistor R24 and byco'nductor B2 through the remainder of the grid and plate circuits oftube section V3A just above mentioned. Current also ows -from theadjusted setting of potentiometer R17 through a resistor R39 inelectrical parallel with a crystal diode CRS which charges a capacitorC7 and then passes through section V7B of a `dual triode tube andconstituting the Voltage Comparator 15. From such tube the current thenows to a common cathode resistor R41 and thence by the aforesaidconductor 29 and resistor R55, the negative bias conductor B2, thenthrough the 450 Volt Bias Supply and positive bias conductor B1 which isalso negative supply conductor L2, thus completing the circuit throughVoltage Comparator tube section V7B which is now conductive at thistime. A current path is also simultaneously established directly to theplate of tube section V7B from positive supply conductor L1 through aresistor R15. Tube section V7A of Voltage Cut-Oli Leveler 17 is likewiseconducting at this time since the voltage impressed on its grid bypotentiometer R36 is above the voltage at the lower end of cathoderesistor R41. The plate of tube section V74 is connected directly to thepositive bias supply conductor B1 while its cathode is connected throughcommon cathode resistor R41, conductor 29 and resistor R55 to thenegative bias supply conductor B2. Thus tube section V7A of the Cut-OttVoltage Leveler 17 is supplied entirely from the 450 Volt Bias Supply:while its other section V7B is supplied from both the 450 Volt BiasSupply and the 450 Volt Supply with their cathodes being common to eachother 7 and set at the same potential by adjustment of potentiometerR36.

Assuming now that the machine has indexed a lamp 14 into its etteringstation, the cam-operated switch 24 will then open during the 1.6seconds rotation of the high surface of such cam switch when the lamp 14is of the gettering station7 as shown in FIG. 2. At this time thetrigger pulse generator S producing its aforesaid 500 pulses per secondis rendered operative with a current pulse flowing 'by way of conductors25 and 2d as well as resistor R56 to develop a voltage across a resistorR57. The voltage thus developed across resistor R57 is a negative pulseand hence crystal diode CR1 is rendered conductive thus lowering thepotential on the plate of tube section V1A from that previously suppliedfrom positive supply-conductor L1. The coupling of capacitor C1 to theplate of V1A lowers the potential on the grid of tube section V1B whichdecreases the flow of current through this tube section V1B and thecommon cathode resistor R20 which thus lowers the potential on both thecathodes of tube sections V1A and VliB.

This lowering of the potential on the cathode of ON tube section V1Atends to make the potential impressed on its grid appear to go positiverelative to the cathode thereby causing this section V1A to becomeconductive and causing a voltage drop to occur through plate loadresistor R3 with attendant lowering of the plate potentlal. This lowerpotential is again transmitted to the grid of ,ON tube section V1B bycapacitor C1 but greatly amplified by the action of section VlA, so thatthis still lowered potential on the grid causes the cathode of sectionVlB to descend even further carrying with it the potential on thecathode of tube section V1A and resulting in vthe latter becoming evenmore vigorously conductive until it becomes saturated whereby tubesection V1B is then cut-off, i.e. becomes non-conductive. When thelatter tube section V1B is completely cut-off there is no longer anycurrent flow through resistor R5 and hence the potential on the plate ofthis tube section VfB rises to the 450 volts of supply conductor L1.This increased potential causes the tiow of current through OR gateresistor R7 to cease because both sides of the crystal diode CR2 are nowat very nearly the same potential.

However, this cessation of current flow through resistor R7 causes agreat rise in the potential then impressed on the grid of OR tubesection V2A which being a cathode follower raises the voltage of thecathode due to the increased current flow through resistor R22. The gridof current regulator and feedback amplifier tube V4 is raised the samenumber of volts as that of the cathode of the cathode-follower tube V2Awith the difference in voltage from the beginning to the top of thepulse being practically the same in each case except that the constantvoltage drop across resistor R21 by the action of tube V6 causes thegrid of the regulator tube V4 to start from its low negative cut-offvoltage when the pulse comes through the cathode follower tube V2A andrise to a sufficiently high voltage to cause the current regulator and'feedback amplifier tube V4 to become conductive. Upon tube V4 becomingconductive a current flows from the 700 Volt Supply causing a voltage todevelop across cathode resistor R43. Since the lower end of resistor R43is connected by conductor 22 to negative supply conductor L2, and thegrid of tube V4 is likewise connected to this same supply conductor L2by means of conductor 23 and resistors R21 and R22, this ow of currentthrough R43 causes the cathode of tube V4 to rise in voltage above thatof its grid. T his tends to reduce and thereby stabilize the current ata level as determined by the magnitude of the voltage impressed on thegrid of tube V4.

The current of about 0.15 amperes flowing through the current regulatorand feedback amplifier tube V4 to the lamp 14 during each pulse ismaintained constant by the circuits connected to the resistor R43 whichdetermine the voltage developed thereacross, with the height of currentamplitude of the pulse controlled by setting of such resistor R43. Atthis point following initiation of the pulse from the trigger pulsegenerator 5, the only tubes that have changed their operating statusfrom the pre-pulse state are ON tube section VllA and tube V4 of CurrentRegulator 12 which have altered from non-conducting to conducting. Theinitial pulses supplied to the lamp 14 from the 700 Volt Supply undercontrol of the tube V4, break into arc discharges but are so few innumber and of such extremely short duration as to not be detrimental.The current thereafter passes through the filament, in the manner shownby the VOLTAGE curve of FIG. 3. These initial pulses are insufficient todevelop the desired 300 volts across the lamp 14 being getter fiashedand so such pulses continue for intermittent periods of 0.44milliseconds duration as shown by the CURRENT curve of FIG. 3. Suchperiod is determined by the resistor R4 and a capacitor C1 together withthe setting of a potentiometer Rid for tube V1 and lasts for 0.44milliseconds unless 300 volts is developed across the lamp filaments, atwhich time the latter will have reached its maximum temperature of 2100"C. so that thereafter the pulse periods decrease to less than 0.44milliseconds, all as seen in the curves of FIG. 3.

Inasmuch as the pulse started, as previously mentioned, when a negativepotential was impressed by capacitor C1 on the grid of ON tube sectionV1B, the pulse lasts during recharging of this capacitor C1 throughresistor R4 until the potential on the grid thereof reaches a valuesufficient to cause tube section V1B to again start to conduct. As thisoccurs the cathode of section V1B begins to rise in voltage, because ofthe increased current flowing through resistor Ritt, and such rise involtage is also impressed on the cathode of ON tube section V1A whichtends to cut-off this latter section. As less current therefore flowsthrough section V1A, less current fiows through resistor R3 whichsupplies such tube section, thereby causing the potential on the plateof section V1A to rise. Since this rise in potential is coupled by thecapacitor C1 to the grid of tube section ViB, this causes such sectionto conduct even more vigorously with increased current iiow throughresistor R5 and tube section V1B. This increased current fiow throughthis resistor R5 lowers the plate potential as tube section VlB againbecomes fully conductive. Such conduction of section V113 increases thecurrent through cathode resistor R20 which raises the cathode voltageabove that impressed on the grid as set by the potentiometer R16 therebyrendering tube section VlA non-conductive and terminating the ON pulse.

Assume that the voltage across the filament of lamp 14 has now reachedthe 300 volts, as was set by the cutoff adjustment of potentiometer R36.This voltage is reached when the preset controlled current pulses haveraised the filament temperature to approximately 2100D C. and thusincreased the hot resistance to the point of developing 300 volts whenthe constant current pulse fiows therethrough and it is desired tomaintain this 2100L7 C. temperature to the end of the 1.6 second getteriiashing period. While ON tube section V1A is conducting, the currentregulator and feedback amplifier tube V4 will likewise be conductingwith a constant flow of current from the 700 Volt Supply7 heating thefilament of lamp 14 and hence increasing its resistance. This constantcurrent fiows through the filament with increased resistance causes auincrease in the voltage thereacross as the temperature of the filamentrises, and such voltage increase lowers the voltage on the negative sideof the 700 Volt Supply relative to that on the common conductor Bl-LZsince current regulator and feedback amplifier tube V4 is part of thatfeedback arrangement. Accordingly, when the voltage on the negative sideof the "700 Volt Supply drops below the voltage set by the Cut-offVoltage Leveler potentiometer R36, the capacitor C15 rapidly 'dischargesthrough crystal diode CR4 which voltage drop is Sensed by VoltageComparator tube section V7B and its grid then becomes negative withrespect to the cathode thereof.

However, the grid of Cut-oit Voltage Leveler tube section V7A isde-coupled by resistor R49 from crystal diode CR4 and is maintained atits original voltage by the charge on capacitor C16 and the isolationprovided temporarily by resistor' R40. Hence there is conduction fromthe common conductor B1-L2 to the plate of tube section V7A and throughsuch tube to the resistor R41 which holds the cathods of both tubesections V7A and VB at a relatively iixed potential. The grid of tubesection V7B being carried downward in voltage cuts oit conductionthrough this tube section with an attendant rise of the voltage on itsplate due to a decrease in current flow through plate-supply resistorR15. This voltage rise is accordingly conducted as a positive pulsethrough capacitor C7 to the grid of OFF tube section VSB which had beenpreviously rendered non-conducting by the previously describedmultivibrator action. Although section VSB had initially beennon-conducting because the potential of its grid was below thatimpressed upon its cathode, the positive pulse now supplied to the gridby capacitor C7 renders such OFF tube section VSB conductive, with thesame ensuing regenerative action as was hereinbefore described relativeto ON generator multivibrator tube V1, to cut-oirt tube section VSA.

When OFF Square Wave Generator tube section VSA is thus renderednon-conducting the reduced current llow through resistor Rit) causes thevoltage to rapidly rise on the plate of section VSA and being a positivepulse is impressed through the capacitor C2 and a resistor R9 upon thegrid of OR gate tube section VZB thereby rendering such sectionconductive. A plate current accordingly now lioWs through the resistorR8 which thereby lowers the voltage on the plate and causing a currentto then flow through the resistor R7 and the crystal diode CRS to theplate of section VZB due to the lower voltage thereon. The flow of`current thus ensuing through resistor R7 and diode CRS causes a voltagedrop across resistor R7 which lowers the voltage on the grid of OR gatetube section V2A even though the plate of ON tube section V1B is stillat a high potential and such section is then non-conducting. Thisvoltage decrease on the grid of section V2A reduces the current liowingthrough. resistor R22, which is further lowered by the constant voltagedrop through resistor R21, resulting in a drop in the voltage on thegrid of current regulator and feedback amplifier tube V4 below itscut-oli thereby terminating current iiow through the filament of lamp14.

lt is thus seen that the OR gate 9 comprising the cathode follower tubesection V2A operates to cause transmission of a pulse through the lamp14 only when section V1B of the ON square wave generator and section VZBof the OR gate are both non-conducting. Also the gate comprising theresistor R7 and crystal diodes CRZ and CRS remains closed as long as OFFtube section VSA is non-conducting but as capacitor C17 rechargesthrough potentiometer R12 the potential on the grid of section VSA risesthereby rendering such tube section again conductive. The resulting iiowof current through load resistor R and OFF tube section VSA causes avoltage drop across load resistor R16 which is coupled by capacitor C2and resistor R9 to the grid of OR tube section VZB, so that such voltagedrop on the grid re turns tube section VZB to its normal non-conductingstate.

It is also to be noted that the time constants of the capacitor C17 andthe setting of potentiometer R12 is such that the OFF square Wavegenerator comprising the multivibrator tube VS will remain in thecondition of section VSA non-conducting and section VSB conducting,until after the ON generator 7 comprising the multivibrator tube V1 hasreturned to its normal state with section VlB conducting. This operationis to prevent any possibility of a double pulse because if OFF tubesection VSA returned to its normal conducting state while ON tubesection V1B was still non-conducting a narrowed second pulse couldotherwise occur for the unexpired duration of the normal ON pulse. HenceOFF section VSB is timed to remain in a conducting state thereby causingOR section VZB to conduct until ON section VIB has returned to itsnormal conducting condition. This allows tube sections VSB and VZB tosafely return to their respective normal non-conducting conditionsbecause the plate of ON7 tube section V1B is no longer at a highpotential ready for a pulse and the entire circuit is again at itspre-pulse condition as previously described awaiting another pulse fromthe trigger pulse generator 5.

Should the pulse fail to cause the voltage across the lamp 14 to rise to30() volts, or Whatever such voltage has been preset by potentiometerR36, the circuit remains as previously described with repetition of thepulse until the preset voltage for the lamp 14 is reached, since thegate consisting of resistor R7 and crystal diodes CRZ and CRS is closedoli until resumption of ON section V1B conduction by recharging ofcapacitor C1 through resistor R4. In the event any subsequent pulseshould cause the voltage across the lamp 14 to exceed the set cut-ottvoltage of 300 volts, then Voltage Comparator tube section V7B willagain become non-conducting causing OFF section VSB to become conductingalong with that of OR tube section V2B thereby stopping current iiowthrough the gate, comprising the previously mentioned crystal diode CRSand resistor R7, and terminating the pulse. A variation in the durationof the ON pulse within certain limits is obtained by adjustment of thepotentiometer R16 While the length of time in which the OFFmultivibrator tube section VSB is conducting can be controlled byselecting the voltage supplied to its grid through adjustment ofpotentiometer R17. After the lamp 14 has been thus getter flashed, themachine indexes such ashed lamp out of the getter flashing station and anew lamp is indexed into such station with the trigger pulse from thegenerator 5 being again interrupted by closing of the previouslymentioned camoperated switch 2d.

After getter flashing in accordance With the present invention, the lamp14 may be further processed, if desired, by applying a color filtercoating over the envelope portion thereof. Since the ilament iscompletely unrecrystallized and is tough, the lamp 14 may be machinepacked or sold loose from bins or store counters without fear ofbreakage due to brittle filaments. When the lamp is first operated bythe user, the lilament will recrystallize.

As a speciiic example for processing a miniature lamp in accordance withthe present invention, 0.02 milligram of red phosphorus getter is placedonto the filament of a 7 watt C-71/2 multiple-type Christmas lamp beforethe mount is sealed to the lamp envelope. After the lamp is evacuated,sealed, and the base ailixed to the envelope neck, the getter is flashedfrom the filament in accordance with the present invention.

The lamp 14, as shown in FIG. 2, is generally standard tn that itcomprises an envelope 30, conventional filamentsupporting stem mount S2sealed to the envelope neck, and lead-in wires 34 sealed through thestem and supporting the filament 36. The lead-in wires 34 connect to thelamp base SS. An additional support wire 40 supports the lilament S6 atits mid-point. The iinished lamp is unusual in that the tilament iscompletely unrecrystallized and is completely free from any adheringgetter material, and yet the lamp envelope also encloses the reactionproducts of getter material liashed from direct contact with the ilamentby self-resistance heating of same. These reaction products of gettermaterial will comprise phosphoruscontaining compound, in the case of thespecific red phosphorus material considered hereinbefore, although othergetter materials may be substituted for the red phosphorus exampleconsidered hereinbefore. Other materials such as aluminum oxide may alsobe flashed from the filament along with the phosphorus, and the use of asupplemental aluminum oxide filament flashed material is known.

In the case of miniature-type lamps, it is preferred that the filamentbe completely unrecrystallized, as is readily determined by examiningits microstructure. It should be understood, however, that in somecases, it may be desirable to flash the filament so that some incipientfilament recrystallization takes place. The present method and apparatuscan also be used to getter flash a lamp in this manner simply by raisingthe getter flashing temperature a small amount.

It should be understood that the specific flashing apparatus asdescribed hereinbefore is subject to considerable modification. Themethod could also be practiced by hand by modifying the constant currentpulses so that heating of the filament occurs at a slower rate. rfhe il(drop developed across the filament, as it is heated up, could then bemonitored and the generator manually adjusted to vary the duration ofthe output of the pulse constant current pulses to maintain the filamentat its flashing temperature.

It should thus be apparent to those skilled in the art from theforegoing that an electronic flashing control system for getteringelectric lamps has been herein provided in which a constant current issuppled to the lamp during flashing of the getter. Moreover, the systemprovides for a very rapid rise in the voltage across the lamp until apreselected temperature maximum is reached after which such temperatureis held substantially at such preselected value to thus maintain thefilament of the lamp at a constant temperature during getter flashing toprevent recrystallization of such filament. By such accurate control ofcurrent, temperature and voltage, the time required to getter flash thelamp is substantially reduced from that heretofore required therebyproducing a higher quality lamp at reduced manufacturing cost.

Although one embodiment of the present invention has been herein shownand described it is to be understood that still further modificationsthereof may be made without departing from the spirit and scope of theinvention.

I claim as my invention:

1. An electronic flashing control system for rapidly getter flashingelectric lamps Without rccrystallization of the filament thereofcomprising:

(a) means operable to apply constant current pulses through the filamentof the electric lamp being getter flashed to produce a predeterminedvoltage drop across said lamp,

(b) means operable to maintain said predetermined voltage drop acrosssaid lamp constant for a preselected period of time to cause thetemperature of said filament to remain at a substantially uniformdesired value during getter flashing of said lamp to preventrccrystallization of said lamp filament, and

(c) means operable after the lapse of a definite period of time torender said system ineffective during transfer of a flashed lamp out ofits getter flashing position and a new lamp into such position.

2. An electronic flashing control system for rapidly getter flashingelectric lamps without recrystallization of the filament thereofcomprising:

(a) means operable to apply constant current pulses of preselectedfrequency and duration through the filament of the electric lamp beinggetter flashed to heat said filament and rapidly produce a voltage dropof predetermined magnitude across said lamp,

(b) means operable to maintain said voltage drop of predeterminedmagnitude across said lamp constant for a preselected period of time tocause the temperature of said filament to remain at a substantiallyuniform desired value during such preselected period of time to preventrecrystallization of said lamp filament, and

(c) means operable after the lapse of such preselected period of time torender said system ineffective during transfer of a flashed lamp out ofits getter flashing position and a new lamp into such position.

3. An electronic flashing control system for rapidly getter flashingelectric lamps without recrystallization of the filament thereofcomprising:

(a) a source of supply including a current regulator and feedbackainplier tube for heating the filament of the electric lamp being getterflashed,

(b) control means connected to said current regulator and feedbackamplifier tube and operable to cause said source to supply constantcurrent pulses of preselected frequency and duration to said filament torapidly produce a voltage drop of predetermined magnitude across saidlamp,

(c) comparator and cut-off means connected to said source of supply andto said control means and operable to cause said control means tomaintain the magnitude of the voltage drop across said lamp constantwith production of a constant preselected temperature of said filamentto prevent recrystallization of the latter during gettering of saidlamp, and

(d) means operable after the lapse of a predermined period of time torender said system ineffective during transfer of a flashed lamp out ofits getter flashing position and a new lamp into such position.

4. A electronic flashing control system for rapidly getter flashingelectric lamps without recrystallization of the filament thereofcomprising:

(a) a source of supply including a controlling amplifier tube andoperable to heat the filament of the electric lamp being etter flashedto a predetermined temperature,

(b) a control circuit connected to said controlling amplifier tube tooperate the latter and cause said source to supply constant currentpulses of preselected frequency and duration to the filament of saidlamp being getter flashed to rapidly produce a voltage drop across saidlamp of predetermined magnitude,

(c) a comparator and cut-olf circuit connected to said source of supplyand to said control circuit and operable to cause said control circuitto maintain said controlling amplifier tube operative and hence thevoltage drop of predetermined magnitude at a constant value to produce aconstant preselected temperature of said lament and preventrecrystallization of the latter during getter flashing of said lamp, and

(d) switch means operable after the lapse of a predetermined period oftime during which said filament temperature has been maintained constantto then render said system ineffective during transfer of a flashed lampout of its getter flashing position and a new lamp into such position.

5. An electronic flashing control system for rapidly getter flashingelectric lamps without reci'ystallization of the filament thereofcomprising:

(a) a circuit for energizing the lamp to be getter flashed including acurrent regulator and feedback amplifier tube and operable to causeenergization of said lamp from a high voltage source of supply,

(b) a high frequency trigger pulse generator for triggering a train ofpulses at a predetermined frequency during gettei'irig of said lamp,

(c) an ON square wave generator including a multivibrator tube operableby the pulses from said trigger pulse generator to emit a square wavesignal pulse of predetermined length,

(d) a control gate circuit including a cathode follower tube andoperable by the signal pulse of predetermined length from said squarewave generator to cause a constant voltage pulse to be impressed Y uponsaid current regulator and 'feedback amplifier tube to render itoperable vto cause energization of said lamp with a constant currentpulse of the same duration as that of said square wave pulse; and

`(e.) a voltage comparator and cut-off circuit, including the currentregulator `and feedback amplilier tube of said lamp energizing circuitand a triode tube, and operable in response to the voltage across saidlamp reaching a preselected value to cause current low through saidtriode tube with attendant operation of said control gate circuitcausing deh energization ofsaidlamp.

6. An electronic flashing control system for rapidly getter ilashingelectric lamps without recrystallization of the filament thereofcomprising:

(a) a circuit for energizing the lamp to rbe getter flashed including vacurrent regulator `.and feedback amplifier tube and operable to causeenergization of vSaitllarilr, a `(b) a high frequency trigger pulsegenerator for trig gering a train of pulses atapredetermined frequencyduring gettering `of said lamp,

(c) an ON square wave generator including fa multi- `vibrator tubeoperable `bythe pulses from said trigger pulse generator to emit asquare wave signal pulse of predetermined length, i'

(d) a control gate `circuit including acathode follower tube :andoperable iby the signal pulse of predetermined length from said squarewave generator to cause a constant Voltage pulse to be vimpressed `uponsaid current regulator Aand feedback ampli-fier tube to render itIoperable to cause energization of said lamp with a constant currentpulse of the same duration as that of said square Waveipulse;

(e) la voltage comparator and cut-off circuit, `including the currentregulator and vfeedback amplifier tube of said lamp energizing circuitand a dual triode tube, and operable in 4response tothe voltage vacrosssaid lamp reaching -a preselected value to cause current llow throughsaid dual triode tube;

(f) andan OFF square wave generator including a multivibrator tubeconnected to said control gate circuit and to said voltage comparatorand cut-olf circuit and operable `in response to current ilow throughsaid latter circuit to cause said control gate circuit to render saidcurrent regulator and -feedback amplier tube non-conductive withdeenergization of said lamp whenever the voltage developed by theconstant current pulse across said lamp exceeds its presetvalue wherebycurrent `ilow through said `lamp andthe temperature of its Vfilament ismaintained constant for a preselected time period to expedite getterflashing of said lamp and preclude recrystallization of its filament.

7. An electronic `flashing. control system `for rapidly getter flashingelectric lamps without recrystallization of the filament thereofcomprising:

(a)` a circuit for energizing the lamp to be getter flashed including acurrent regulator and feedback amplifier ltube and operable to causeenergization of said lamp from a high voltage source of supply,

(-b) `a high frequency trigger pulse generator for triggering 1a trainof pulses at a predetermined frequency of 5approximately `500 pulses persecond land Vfor a duration )of about :1.6 seconds during gettering ofsaid lamp,

(c) arr-ON square waive generator including a multivibra-tor tubeoperable by the pulses from saiditrigger pulse generator `tov emit aAsquare wave signal pulse of predetermined length,

(d) a control .gate circuit including a cathode V:follower tube andoperable by the .signal pulse rof'vpredetermined length from said square:wave generator to cause a ,constant voltage pulse I,to he impressedupon said cunrent regulator and feedback amplifier tube vto 4render itoperable to cause energization of said lamp with a constant currentpulse 'of the same duration .as that ofsaid square wave pfulse;

V(e) a voltage comparator and cut-off circuit, including the current`regulator and .feedback amplifier tube of saidlamp energizing circuitand a dual triode tube, arid operable in response to the voltage ac-rosssaid lamp reaching a preselected value-to cause current flow throughsaid dual triode tube;

(f) and an OFF square wave `generator including a Amulti-vibrator tubeconnected to said control gate circuit and `to said voltage comparatorand cut-olf circuit and operable lin response to current tlow throughsaid latter circuit to cause said control gate circuit -to rendersaidcurrent regulator and feedback amplifertube non-conductive withdeenergization of said lamp whenever the voltage developed by theconstant current pulse across s-aid lamp exceeds its preset valuewhereby current flow through said lamp and the temperature Vof itsfilament Ais maintained constant for a preselected time period toexpedite getter dashing of said lamp and preclude recrystallization ofits Illa-ment.

8. An electronic flashing control system for rapidly getter llashing`electric lamps without recrystallization of the filament thereofcomprising:

(a) a circuit -for energizing the 4lamp to be getter flashed including acurrent regulator andA feedback amplifier tube and operable to causeenergization of said lamp,

(b) a high frequency trigger pulse generator for triggering a train ofpulses at a'predetermined Yfrequency during gettering of said lamp,

(c) an ON square wave generator including -a ymultivibrator tubeoperable by the pulses from said trigger pulse generator to emit fasquare wave signal pulse of predetermined length,

(d) a control gate circuit including a cathode follower tube and aconstant cunrentregulator tube and operable by the signal pulse ofpredetermined length from `said square wave'generator to cause aconstant vo1tage pulse to be impressed by said `con-trol gate circuitupon the current regulator and feedback amplilier tube of said lampenergizing circuit to render such tube operable to cause energization ofsaid lamp g with 'a constant current pulse of the same duration as thatof said square wave pulse;

(e) a voltage comparator AFand cut-off circuit, including the currentregulator and feedback amplifier tube of said lamp energizing circuitand a dual triode tube, and operable in response to the voltage acrosssaid lamp reaching a preselected value tocause current llow through saiddual trio-de tube;

(f) and :an OFF square wave generator including a multivibrator tubeconnected to said control gate circuit and to said voltage comparatorfand cut-off circuit and operable in response to current ilow throughsaid latter circuit to cause said control gate circuit to render saidcurrent regulator and feed-back `amplifier tube non-conductive withdeenergization of said lamp until after cessation of the square wavesignal pulse of predetermined length 'than being Supplied, to -saidcontrol gate cirucit by said ON square `Wave generator, whereby currentflow through -said lamp tand the temperature of its filament `ismaintained constant lfor a preselected time period to expedite getterllas'hing of said lamp and preclude recrystallization of its filament.

`9. An electronic flashing control system for rapidly getter ilashingelectric lamps without -recrystallization of the filament thereofcomprising: v

(a a circuitfor energizing the lamp to be getter flashed including acurrent `regulator and feedback amplier tube and -operable to`causerenergiz'atior'l of said lamp,

` Lb!) a'h'gh frequency trigger .pulse generator fortriggering a trainof pulses at a predetermined frequency during gettering of said lamp,

(c) an ON square wave generator including a multivibrator tube having one `side connected to a supply source and normally conductive While itsother side is non-conductive until pulses from said trigger pulsegenerator are Aimpressed thereon to cause a reversal in the conductivityof both sides of said-multivibrator tube with attendant production lof asquare wave signal pulse of predetermined length, l

(d) a control gate circuit including a cathode follower tube and aconstant current regulator tube and operable by the signal pulse ofpredetermined length from said square wave generator to cause a constantvoltage pulse to be impressed by said control gate circuit upon thecurrent regulator and feedback amplifier tube of saidrlamp energizingcircuit to render such tube operable to cause energization of said lampwith a constant current pulse of the same duration as that of saidsquare wave pulse;

(e) a voltage comparator and cut-off circuit including the currentregulatorand feedback amplifier tube of said lamp energizing circuit anda dual triode tube, and operable in response to the voltage across saidlamp reaching a preselected value to cause current flow through said dual triode tube;

(f) and an OFF square wave generator including a multivibrator tubeconnected to said control gate circuit and to said voltage comparatorand cut-off circuit and operable in response to current iiow throughsaid latter circuit to .cause said control gate circuit to render saidcurrent regulator and feedback a-mplifier tube non-conductive withdeenergization of said lamp whenever the voltage developed by theconstant current pulse across said lamp exceeds its preset value andwith such deenergization lasting until after ces- "sation of the squarewave signal pulse of predetermined length then being supplied to saidcontrol gate circuit by said ON square wave generator, whereby currentfiow through said lamp and the temperature of its filament ismaintainedconstant for a preselected time period to expedite getter fiashing ofsaid lamp and preclude recrystallization of its filament.

10. An electronic fiashing control system for rapidly getter flashingelectric lamps without recrystallization of the filament thereofcomprising:

(a) a circuit for energizing the lamp to be getter liashed including acurrent regulator and feedback amplifier tube and operable to causeenergization of said lamp,

`(b) a high frequency trigger pulse generator for triggering a train-ofpulses at a predetermined frequency .during gettering of said lamp,

(c) an ON square wave generator including a multivibrator tube havingone side connected to a supply sourceand normally conductive-while itsother side is non-conductive until pulses are impressed thereon fromsaid trigger pulse generator to cause a reversal in the conductivity. ofboth sides of said multivibrator tube with attendant production of asquare wave sig- .nal pulse of predetermined length,

(d) a control gate circuit including a cathode follower tube having oneside'thereof conductively operable to normally pass a small current tomaintain its cathode just a few volts above its grid potential, and saidcathode-follower side being operable with a heavier .-current flow uponthe ,application of a square wave signalpulse of predetermined lengthupon its grid from said square wave generator to cause a constantvoltage pulse to nbe impressed by said control gate circuit upon thecurrent regulator and feedback amplifier tube of said lamp energizingcircuit to render such tube operable to causecnergization of said lampwith a constant current-:pulse-of the same duration as`thatofsaidfsquare wave pulse;

(e) Ia voltage comparator and cut-off circuit, including l5 the currentregulator and feedback amplifier tube of said lamp energizing circuitand a dual triode tube, and operable in response to the voltage acrosssaid lamp reaching a preselected value to cause current iiow throughsaid dual triode tube;

(f) and an OFF square wave generator including a multivibrator tubeconnected to saidl control gate circuit and to said voltagecornparatorand cut-off circuit and operable in response to current flow throughsaid latter circuit to cause said control gate circuit to render saidcurrent regulator and feedback amplifier tube non-conductive withdeenergization of said lamp whenever the voltage developed by theconstant current pulse across said lamp exceeds its preset value andwith such deenergization lasting until after cessa- Vtion of the squarewave signal pulse of predetermined length then being supplied to saidcontrol gate circuit by said ON square wave generator, whereby currentfiow through said lamp and the temperature of its filament is maintainedconstant for a preselected time period to expedite getter flashing of4said lamp and preclude recrystallization of its filament.

11. An electronic flashing control system for rapidly getter flashingelectric lamps without recrystallization of the filament thereofcomprising:

(a) a circuit for energizing the lamp to be getter flashed including acurrent regulator and feedback amplifier tube and operable to causeenergization of said lamp,

(b) a high frequency trigger pulse generator for triggering a train ofpulses at a predetermined frequency during gettering of said lamp, t

(c) an ON square wave generator including a multivibrator tube havingone side connected to a supply source and normally conductive while itsother side is non-conductive until pulses are impressed thereon fromsaid trigger pulse generator to cause a reversal in the conductivity ofboth sides of said multivibrator tube with attendant production of asquare Wave signal pulse of predetermined length,

(d) a control gate circuit including a constant current regulator tubeand a cathode follower tube, said cathode follower tube having one sidethereof conductively operable to normally pass a small current tomaintain its cathode just a few volts above its gridvpotential, andhaving its otherl side operable with a heavier current flow upon theapplication of a square wave signal pulse of predetermined length fromsaid square wave generator to cause a constant voltage pulse to beimpressed by said control gate circuit upon the current regulator andfeedback amplifier tube of said lamp energizing circuit to render suchtube operable to cause energization of said lamp with a constant currentpulse of the same duration as that of said square wave pulse;v

(e) a voltage comparator and cut-off circuit, including the currentregulator and feedback amplifier `tube of said lamp energizing circuitand a dual triode tube, and operable in response to the voltage acrosssaid lamp reaching a preselected value to cause said dual triode tube togenerate a positive pulse;

(f) and an OFF square wave generator including a multivibrator tubeconnected to said control gate circuit and to said voltage comparatorand cut-off circuit and operable in response to the current pulsethrough said,latter circuit to cause said control gate circuit to rendersaid current regulator and feedback amplifier tube non-conductive withdeenergization of said lamp until after cessation of the square wavesignal pulse of predetermined length then being supplied to said controllgate circuit by said ON square wave generator, whereby current flowthrough said lamp and temperature of its filament is maintained constantfor a preselected time period to expedite getter flashing of said lampand preclude recrystallization of its filament.

12. An electronic fiashing control system for rapidly getter flashingelectric lamps without recrystallization of the filament `thereofcomprising:

(a) a circuit for energizing the lamp to be getter fiashed including acurrent regulator and feedback amplifier tube and operable to causeenergization of said lamp from a high voltage source of supply,

(b) a high frequency trigger pulse generator for triggering a train ofpulses at a predetermined frequency during gettering of said lamp,

(c) an ON square Wave generator including a multivibrator tube havingone side connected to a supply source and normally conductive while itsother side is non-conductive until pulses are impressed thereon fromsaid trigger pulse -generator to cause a reversal in the conductivity ofboth sides of said multivibrator tube with attendant production of asquare wave signal pulse of predetermined length,

(d) a control gate circuit including a constant current regulator tubeand a cathode follower tube, said cathode follower tube having one sidethereof conductively operable to normally pass a small current tomaintain its cathode just a few volts above its grid potential, andhaving its other side operable with a heavier current fiow upon theapplication of a square Wave signal pulse of predetermined length fromsaid square wave generator to cause a constant voltage pulse to beimpressed by said control gate circuit upon the current regulator andfeedback amplifier tube of said lamp energizing circuit to render suchtube operable to cause energization of said lamp with a constant currentpulse of the same lduration as that of said square Wave pulse;

(e) a voltage comparator and cut-off circuit, including the currentregulator and feedback amplifier tube of said lamp energizing circuitand a dual triode tube having both sides thereof normally conductive,said voltage comparator and cut-off circuit being operable, in responseto the voltage across said lamp reaching a preselected value andrendering one side of said dual triode tu-be non-conductive, to generatea positive pulse;

(f) and an OFF square wave generator including a multivibrator tubeconnected to said control gate circuit and to said voltage comparatorand cut-off circuit and operable in response to the current pulsethrough said latter circuit to cause said control gate circuit to rendersaid current regulator and feedback amplifier tube non-conductive withdeenergization of said lamp Whenever the voltage developed by theconstant current pulse across said lamp exceeds its preset value andwith such denerg-ization lasting until after cessation of the squareWave signal pulse of predetermined length then being supplied to saidcontrol gate circuit by said ON square Wave generator, whereby currentflow through said lamp and the temperature of its filament is maintainedconstant for a preselected time period to expedite getter flashing ofsaid lamp and preclude recrystallization of its filament.

13. The method of rapidly getter flashing the filament of an electriclamp without recrystallzation of the filament thereof comprising:

(a) subjecting the filament of such lamp lto constant current electricalpulses of preselected frequency and duration to rapidly produce avoltage drop of predetermined magnitude across said lamp,

(b) controlling the time of application of the constant current pulsesto the filament to produce a constant voltage drop of preselectedmagnitude across the lamp as a measure of a preselected ensuingtemperature of the filament to prevent recrystallization thereof duringfiashing of the lamp, and

(c) interrupting the application of the constant current pulses ofpreselected frequency and duration to the lamp filament after the lapseof the: preselected period of time and during transfer of a flashed lampout of its getter flashing position and a new lamp into such position.

14. The method of rapidly getter flashing the filament of an electriclamp Without recrystallization of the filament thereof comprising:

(a) applying constant current electrical pulses of preselected frequencyand duration to the filament of the lamp for a period of time sufficientto rapidly produce a voltage drop of predetermined magnitude across saidlamp,

(b) decreasing the period of time during which each constant currentpulse is applied to the filament once the voltage drop across said lamphas reached the predetermined magnitude to thus maintain such voltagedrop constant and as a measure of an ensuing constant lamenttemperature, and

(c) discontinuing the application of the constant current -pulses to thelamp filament after the lapse of a preselected period of time duringwhich such filament has been maintained at a constant temperature toprevent recrystallization thereof during fiashing of the' lamp.

15. Apparatus for heating an unrecrystallized filament, which displaysan electrical resistance which increases sharply with temperature, inorder to flash a getter material from said filament Without causing thefilament to recrystallize, which apparatus comprises:

(a) current supply means for passing through said filament a series ofconstant current pulses of predetermined duration and magnitude torapidly heat said filament 'to a predetermined temperature sufficient tofiash said getter material from said filament but insufficient to causesaid filament to recrystallize;

(b) voltage detecting and signalling :means responsive to the IR dropdeveloped across said filament when the constant current pulses arepassed therethrough, and said voltage detecting and signalling meansgenerating a control signal when the IR drop developed across saidfilament reaches a predetermined value signifying that saidpredetermined filament getter fiashing temperature has been achieved;

(c) current pulse control means responsive to the control signalgenerated by said voltage detecting and signalling means to shorten theduration of each constant current pulse passed through said filament bysaid current supply means to decrease the average lwattage consumed bysaid filament by such amount that the resulting IR drop across saidfilament during each such shortened constant current pulse appliedtherethrough is maintained substantially at that predetermined valuewhich indicates that the predetermined filament getter ffashingtemperature has lbeen achieved; and

(d) timing means for controlling said current supply means to passconstant current pulses through said filament for a predetermined timesufficient to completely liash the getter material from said filament.

16. The method of heating an unrecrystallized filament, which displaysan electrical resistance which increases sharply with temperature', inorder to flash a getter material 'Without causing the filament torecrystallize, which method comprises:

(a) initially applying across said filament a series of constant currentpulses of predetermined magnitude and duration;

(b) detecting the voltage developed across said filament during theapplied constant current pulses;

(c) when the detected voltage reaches a predetermined value signifyingthat the filament has achieved a predetermined temperature sufiicient toflash said getter, but insufficient to recrystallize said filament,modifying the appl-led constant current pulse so that the 19 averagevoltage consumed by said filament is just sutiicient to maintain saidfilament at about said predetermined getter flashing temperature; and

(d) continuing to apply across said heated filament such modifiedconstant current pulses to maintain said filament at the predeterminedtemperature required to ash said getter for a sufficient time tocompletely flash said getter.

17. The method of heating an unrecrystallized filament, which displaysan electrical resistance which increases sharply with temperature, inorder to flash a Igetter material 'without causing the filament torecrystallize, which method comprises:

(a) initially applying across the filament al series of current pulsesof predetermined magnitude and duration with a predetermined intervalbetween each pulse to rapidly heat said filament;

(b) detecting the voltage developed across the filament when theconstant current pulses are passed therethrough;

(c) When the detected voltage reaches a predetermined Value signifyingthat the filament has achieved a predetermined temperature sufiicieintto flash said getter, but insufficient to recrystallize said filament,decreasing the duration of each applied constant current pulse by apredetermined amount sufficient to maintain said filament at about saidpredetermined getter flashing temperature; and

(d) continuing to apply across said heated filament such constantcurrent pulses of predetermined shortened duration to maintain saidfilament for a predetermined time at the predetermined temperaturerequired to flash said getter.

References Cited UNITED STATES PATENTS 8/1952 Rockwood 31612 JAMES W.LAWRENCE, Primary Examiner.

Examiners.

S. A. SCHNEEBERGER, Assistant Examiner.

